Solar flares are sudden flashes of increased brightness on the Sun, which eject large amounts of plasma and electromagnetic radiation into space. Astronauts in space are at risk of exposure to intense radiation and energetic particles during solar flare events. The effects on an astronaut’s health depend on the intensity of the solar flare, the amount of shielding around them, and the length of exposure.
What are solar flares?
Solar flares occur when magnetic energy built up in the solar atmosphere is suddenly released. This causes a burst of radiation across the electromagnetic spectrum, from radio waves to x-rays and gamma rays. The initial flash of increased brightness lasts just a few minutes, but it takes hours or days for the ejected plasma and particles to reach Earth. Solar flares are classified based on their x-ray brightness, with X-class flares being the largest and most intense.
The high-energy radiation and energized particles emitted during a flare can have effects on Earth such as disrupting radio communications and causing auroras. They can also pose a significant hazard to astronauts and equipment in space. The risk is highest for astronauts doing spacewalks outside the protective shielding of a spacecraft or space station.
How are astronauts affected by solar flare radiation?
Astronauts exposed directly to a solar flare could experience both short-term and long-term health effects:
- Acute radiation sickness – High doses of radiation from a major solar flare could cause symptoms like nausea, vomiting, fatigue, and skin burns arising within hours or days. Very large doses can damage the gastrointestinal tract, central nervous system, and bone marrow, potentially leading to death.
- Increased cancer risk – Ionizing radiation exposure increases lifetime cancer risk. It can damage DNA and cause genetic mutations that allow cancerous cells to develop later on.
- Degenerative tissue effects – Radiation exposure speeds up cell aging and loss of tissue function. This can lead to problems like cataracts, heart disease, cognitive decline, and nerve damage appearing years later.
- Compromised immune function – Damage to bone marrow and the immune system from radiation can reduce the body’s ability to fight infections for days or weeks.
The specific health impacts depend on the radiation dose absorbed by the astronaut’s body tissues. The skin and organs not protected by bone and muscle receive the highest doses.
How much radiation do astronauts receive?
Radiation exposure depends on the duration of the solar flare event, the flare’s intensity, and the amount of shielding around the astronaut. Here are some examples of radiation doses measured during major solar flare events:
| Event | Astronaut location | Estimated radiation dose |
|---|---|---|
| August 1972 solar flares | Moon (Apollo lunar mission) | 1.2 rem over 20 hours |
| October 1989 solar flares | Space shuttle in low Earth orbit | 0.14 rem over 9 hours |
| January 2005 solar flares | International Space Station | 0.01 rem over 3 days |
For context, the average annual background radiation on Earth is about 0.62 rem. A lethal acute dose is estimated to be around 75 rem delivered over several hours. However, lower doses like 10 rem still carry a 5% risk of eventual cancer death.
How are astronauts protected from solar flares?
NASA and other space agencies take various precautions to protect astronauts from solar flare radiation:
- Spacecraft shielding – Aluminum hulls and other materials provide a barrier against particle radiation.
- Spacesuit shielding – White outer layers reflect photons, while inner layers absorb energetic particles.
- Radiation monitoring – Devices like dosimeters track astronauts’ exposure over time.
- Mission timing – Activities that involve leaving spacecraft are planned for periods of low solar activity.
- Storm shelters – During solar storms, astronauts take refuge in sections with extra aluminum shielding.
- Medications – Drugs can be used to treat radiation sickness symptoms or offset lost immune cell production.
However, no feasible amount of shielding can block all radiation from the largest solar flares. Astronauts on missions beyond Earth’s protective magnetosphere remain at risk.
What are the worst solar flares on record?
Some of the most powerful solar flares and associated events recorded include:
- August 1972 – A series of enormous X-class flares produced solar particle events that exposed Apollo astronauts on the Moon to hazardous radiation levels.
- March 1989 – An extreme geomagnetic storm triggered by strong solar flares knocked out power across Quebec, Canada for 9 hours.
- October 2003 – Multiple X-class flares led to solar energetic particle fluxes high enough to place spacecraft and astronauts at significant risk.
- July 2012 – An ultrafast CME from an X-class flare passed through Earth’s orbit just one week after it occurred, much faster than expected.
- September 2017 – An X9.3 flare was the strongest since at least 1976, emitting a powerful solar particle storm.
The most dangerous solar flares produce sustained x-ray outputs over X20, along with coronal mass ejections (CMEs) with speeds exceeding 2500 km/s. Such extreme events are infrequent, but can subject astronauts in space to acute radiation sickness levels or higher over the course of a mission.
Could a powerful solar flare be deadly for an astronaut?
Yes, a powerful solar flare could potentially be deadly for an astronaut in space if they receive a high enough radiation dose. However, instant death from radiation is very unlikely. Here are some possible consequences from extreme solar flare radiation exposure:
- Acute radiation sickness – Nausea, vomiting, fatigue, skin burns, and changes to blood cells and immune function within hours or days. At very high doses, death may occur within several weeks due to infection, fluid loss, and circulatory collapse.
- Increased lifetime cancer risk – Large radiation doses significantly raise risks for multiple forms of cancer. However, effects would generally not arise for at least several years.
- Degenerative health effects – Radiation exposure accelerates aging, which could lower quality of life in later years. But this occurs gradually, not suddenly.
Astronauts exposed to otherwise lethal acute doses may survive for weeks with medical treatment. But the health impacts could end their career or significantly shorten lifespan. Space agencies aim to avoid these scenarios with proper monitoring and protective measures.
How might a worst-case solar storm affect plans for a manned Mars mission?
A worst-case solar storm could greatly impact plans for NASA’s manned Mars mission goals in the 2030s. Possible effects include:
- More shielding required – To protect astronauts from large flares, heavier spacecraft shielding would be needed, increasing launch costs.
- No viable safe exposure limits – It may be impossible to meet acceptable radiation dose limits on a multi-year round trip Mars mission.
- Increased cancer risk – Large flares could raise lifetime cancer risk above currently allowed thresholds for astronauts.
- More storm shelters needed – Additional shielded areas for astronauts to take refuge during storms would add complexity.
- Mission delays – Launches may need to be restricted to periods of low flare probability, limiting launch windows.
- Less surface exploration – Time spent on the unshielded Martian surface during storms may need to be minimized.
NASA is studying various shielding techniques and scenarios to enable safe Mars missions. But unpredictable extreme solar storm events remain a major hazard that could force delays and higher costs.
Conclusion
Solar flares can expose astronauts in space to dangerous levels of radiation and energized particles. The health impacts depend on the flare intensity and duration of exposure. Major flares could potentially cause acute radiation sickness, increase cancer risk, or contribute to degenerative diseases over time. To protect astronauts, space missions incorporate shielding, monitoring, medical remedies, and other safety practices. But powerful solar storms remain a serious risk that must be considered carefully for any planned manned interplanetary voyages like a future Mars mission.